Which two of the following are not neighbours ?

Concept: In a circular arrangement, two points are neighbours only if they sit immediately next to each other while going around the circle - each point has exactly two neighbours (the one immediately clockwise and the one immediately anticlockwise). A pair with even one point between them is not a neighbour pair.

Application: Reading the diagram clockwise gives the fixed order Q, P, R, T, V, U, S, W (and back to Q). Walking around the circle one step at a time:

1. Q to P: adjacent, so Q and P are neighbours.

2. P to R: adjacent, so P and R are neighbours.

3. R to T: adjacent, so R and T are neighbours.

4. T to V: adjacent, so T and V are neighbours.

5. V to U: adjacent, so V and U are neighbours.

6. U to S: adjacent, so U and S are neighbours.

7. S to W: adjacent, so S and W are neighbours.

8. W back to Q: adjacent, so W and Q are neighbours.

Cross-check: Compare each given pair against this neighbour list.

Only RV fails the adjacency test, so RV is the pair that is not neighbours.